Temperature-Triggered/Switchable Thermal Conductivity of Epoxy Resins

The pronouncedly low thermal conductivity of polymers in the range of 0.1–0.2 W m−1K−1is a limiting factor for their application as an insulating layer in microelectronics that exhibit con-tinuously higher power-to-volume ratios. Two strategies can be applied to increase the thermalconductivity of polymers; that is, compounding with thermally conductive inorganic materials aswell as blending with aromatic units arranged by the principle ofπ-πstacking. In this study, bothstrategies were investigated and compared on the example of epoxy-amine resins of bisphenol Adiglycidyl ether (BADGE) and 1,2,7,8-diepoxyoctane (DEO), respectively. These two diepoxy com-pounds were cured with mixtures of the diamines isophorone diamine (IPDA) ando-dianisidine(DAN). The epoxy-amine resins were cured without filler and with 5 wt.-% of SiO2nanoparticles. En-hanced thermal conductivity in the range of 0.4 W·m−1·K−1was observed exclusively in DEO-basedpolymer networks that were cured with DAN (and do not contain SiO2fillers). This observation isargued to originate fromπ-πstacking of the aromatic units of DAN enabled by the higher flexibility ofthe aliphatic carbon chain of DEO compared with that of BADGE. The enhanced thermal conductivityoccurs only at temperatures above the glass-transition point and only if no inorganic fillers, whichdisrupt theπ-πstacking of the aromatic groups, are present. In summary, it can be argued thatthe bisphenol-free epoxy-amine resin with an epoxy compound derivable from natural resourcesshows favorably higher thermal conductivity in comparison with the petrol-based bisphenol-basedepoxy/amine resins.